Katia Zatuliveter, 26, had affairs with Mike Hancock, a member of the defence select committee, and with a Dutch diplomat, a German Nato official, and a UN worker.

MI5 conducted a “thorough and competent” investigation into Miss Zatuliveter and there were “ample grounds for suspicion”, according to an immigration tribunal.

But they said nothing “suggests, let alone demonstrates,” that Miss Zatuliveter had “exploited her relationships for the purposes of the Russian state.”

They accepted that her activities “would have been of great interest” to Russian intelligence, but said they were also “entirely consistent with her being an ambitious young woman with an intense interest in politics and international relations.”

The Daily Telegraph understands that Miss Zatuliveter plans to return to Russia and launch a political career. She has already engaged an agent to sell her story.

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MI5 accept that she formed “genuine emotional relationships with older men” founded on a common interest in politics and international affairs, and their “humour, sophistication and kindliness,” the panel said.

A personal diary included “excruciating detail” about her attempts to ensnare men and revealed she was an “immature, calculating, emotional and self-centred young woman,” they said.

The panel said they were satisfied that Miss Zatuliveter was not “tasked to seduce” a Dutch diplomat in his thirties, a Nato official aged 50 and Mike Hancock, 65.

They said the relationship with the Dutch diplomat was “little more than a late teenage crush”, that with Mr Hancock was “enduring and genuine on both sides” and with the Nato official was “short, but genuine.”

They said Mike Hancock, the Lib Dem MP for Portsmouth South, who appeared to mix with glamorous Russian and Ukrainian women and was supportive of the Russian government “would have been of long-standing interest to one or more Russian intelligence agencies.”

They added that they did not believe Mr Hancock’s “lengthy and elaborate” explanation about how he warned Miss Zatuliveter not to meet a Russian spy called “Boris” who was based at the embassy in London.

Mr Hancock, the panel said, tried to get Miss Zatuliveter’s attention from the moment he met he in St Petersburg and an entry in her diary showed she was prepared to sleep with him.

But the entries showed that within six weeks she was in love with him and calling him “my darling Teddy Bear.”

She moved to Bradford to study and then moved into his flat in London, but the panel said he finished the relationship in April 2010, “we suspect...at least in part, to avoid the possibility of unwelcome media attention as the election approached.”

Her sister and brother-in-law, with whom she lived in Bradford, did not accept her relationship with Mr Hancock but the panel said: “However odd it might seem, she fell for him.”

The Special Immigration and Appeals Commission (SIAC) accepted her appeal against deportation and she will now be allowed to stay in Britain until her visa expires next August.

“We cannot exclude the possibility that we have been gulled – but, if we have been, it has been by a supremely competent and rigorously trained operative,” the panel said.

Miss Zatuliveter said afterwards that she was “very happy” with the decision and her parents were “ecstatic.” Her tearful sister, Polina, who lives in Chorley, Lancashire, rushed from the court room to ring them when the judgment came through.

Miss Zatuliveter’s father, a former mining engineer turned businessman in the North Caucasus region of Kabardino-Balkaria, told the Daily Telegraph: “Next time they accuse someone of spying and try to deport them perhaps they can make sure they have some evidence, at least the bare minimum.”

“It was a nightmare year,” he said, his voice shaking with emotion. “I was always confident in the UK justice system but there was enormous pressure on it and the tribunal could have caved into that pressure.”